Initial changes in pulpal microvasculature during orthodontic tooth movement: a stereological study.

Any alteration in blood flow or vascular pressure caused by a trauma may damage the pulp tissue. The aim of this study was to evaluate the vascular changes during the initial period of tooth movement. These alterations were assessed in coronal molar pulp tissue of 20 male Wistar rats, 90 days of age, submitted to mesial inclination movement by a closed coil spring, placed from the right maxillary first molar to the maxillary incisors. The animals were divided into three experimental groups of 6, 24, and 72 hours of 0.4 N force application, with five animals in each group, and a control group of five animals without tooth movement. The volume density of blood vessels (V(v)) of the coronal pulp tissue in the experimental groups was calculated by stereology and compared with the control group. The results demonstrated a significant increase in V(v) at 6 hours of 10.2 per cent compared with 7.2 per cent for the control group (P <or= 0.05). At 24 and 72 hours, V(v) was reduced, with values close to those observed for the control group (P > 0.05). These results demonstrate the high capacity of adaptation of the pulp tissue to an aggression, provided the biological limits of tolerance of the pulp are respected.